[giaour]

I've only used this feature with HTTP requests going to a function app, but my understanding was that there is a reverse proxy involved. I have an app with two slots, and both slot domains (<app name>.azurewebsites.net and <app name>-staging.azurewebsites.net) report the same external IP address. You can set up routing rules where a percentage of incoming traffic is forwarded to a specific slot, which would be hard (impossible?) to manage via DNS or ARP tables.